One finding in nutritional science is that resistant starch has important implications for bowel health, in particular health of the large bowel. The beneficial effects of resistant starch result from the provision of a nutrient to the large bowel wherein the intestinal microflora are given an energy source which is fermented to form inter alia short chain fatty acids. These short chain fatty acids provide nutrients for the colonocytes, enhance the uptake of certain nutrients across the large bowel and promote physiological activity of the colon. Generally if resistant starches or other dietary fibre is not provided the colon is metabolically relatively inactive.
There has in recent years been a direction to look at providing for resistant starches from various sources to address bowel health. Accordingly high amylose starches have been developed in certain grains such as maize for use in foods as a means of promoting bowel health.
The physical structure of starch can have an important impact on the nutritional and handling properties of starch for food products. Certain characteristics can be taken as an indication of starch structure including the distribution of amylopectin chain length, the degree of crystallinity and the presence of forms of crystallinity such as the V-complex form of starch crystallinity. Forms of these characteristics can also be taken as indicator of nutritional or handling properties of foods containing these starches. Thus short amylopectin chain length may be an indicator of low crystallinity and low gelatinisation and is also thought to have a correlation with reduced retrogradation of amylopectin. Additionally shorter amylopectin chain length distribution is thought to reflect organoleptic properties of food in which the starch is included in significant amounts. Reduced crystallinity of a starch may also be indicative of a reduced gelatinisation temperature of starch and additionally it is thought to be associated with enhanced organoleptic properties. The presence of V-complex crystallinity or other starch associated lipid will enhance the level of resistant starch and thus dietary fibre.
Lines of barley having high amylose starch contents have been identified in the past. These have only resulted in relatively modest increases in amylose content to a maximum of about 45% of total starch such as in the barley variety known as High Amylose Glacier (AC38). Whilst elevated amylose starches of that type are useful a starch with a higher amylose content still is preferred, and certain other species of grain are bred to have higher amylose content starches with levels in the 90 percentile range. These are very resistant to digestion and bring a greater health benefit.
There is a problem with providing the high amylose starches because known high amylose starches also have a high gelatinisation temperature. Gelatinisation temperature is reflective of the comminution energy required to process such foods. Thus higher temperatures are normally required to process grain or flour to manufacture foods from such grains or starches. Thus generally products having high amylose starches are more expensive. Similarly from the point of view of the consumer longer times and higher temperatures may be required to prepare the manufactured foods, or to make foods from flour having high amylose starches. Thus there is a significant disadvantage in the provision of high amylose starches in foods.
Another nutritional component of the grains and in particular of barley as β-glucans. β-glucans consist of glucose units bonded by β(1-4) and/or β(1-3) glycosidic linkages and are also not degraded by human digestive enzymes which makes them suitable as a source of dietary fibre. β-glucans can be partially digested by endogenous colonic bacteria which fermentation process gives rise to short chain fatty acids (predominantly acetate, propionate and butyrate) which are beneficial to mucosal cells lining the intestine and colon (Sakata and Engelhard Comp. Biochem Physiol. 74a:459-462 (1983))
Ingestion of β-glucan also has the effect of increasing bile acid excretion leading to a reduction in total serum cholesterol and low density lipoproteins (LDL) with a lowering of the risk of coronary disease. Similarly β-glucans act by attenuating excursions in postprandial blood glucose concentration. It is thought that both of these effects are based on the increase of viscosity in the contents of the stomach and intestines.
The composition of foods containing starches and the intimate relationship of those starches with other nutritional or other components can have a significant impact on the nutritional value of those foods or on the functional characteristics of those components in the preparation or structure of the foods.
Whilst modified starches or β glucans, for example, can be utilised in foods that provide functionality not normally afforded by unmodified sources, such processing has a tendency to either alter other components of value or carry the perception of being undesirable due to processes involved in modification. Therefore it is preferable to provide sources of constituents that can be used in unmodified form in foods.
The barley variety MK6827 is available from the Barley Germplasma Collection (USDA-ARS National Small Grain Germplasma Research Facility Aberdeen, Id. 831290 USA). The grain of MK6827 is shrunken and has a highly coloured husk and an elongate shape and, in the hands of the inventors, this grain is very difficult to process including being very resistant to milling. The properties of MK6827 grain had not been characterised before, nor had the nature of the mutation been ascertained nor is it considered suitable for producing food.